Water-resistant alkali metal and alkaline earth metal-containing grease



WATER-RESISTANT ALKALI METAL AND ALKALINE EARTH METAL-CGNTAWIING GREASEHarry J. Worth, Fullerton, Califi, assiguor to Union Oil Company ofCalifornia, Los Angeles, 'Calii'l, a corporaion of California NoDrawing. Application October 6, 1953 Serial No. 384,527

20 Claims. (Cl. 252-423.)

This invention relates to lubricating greases and particularly greaseswhich are resistant to and retain their grease like structure in thepresence of water. More particularly the invention relates to alkalimetal-alkaline earth metal mixed base greases having a large excess ofmetal and being prepared in a certain manner.

Alkali metal soap greases and particularly sodium soap greases arerelatively cheap to prepare because of the simplicity of compoundingprocedures and partic ularly because of the low cost of the metal andthe saponifiable material used in preparing the soaps. However, thesegreases are not suitable in many applications due primarily to theirlack of water resistance, especially at elevated temperatures. Althoughwater-resistant greases have been prepared from various metals andcombinations of metals, greases cause of the high cost of metal and/orsaponifiable material employed, or the greases lack other propertieswhich are desirable and which are normally possessed by sodium or otheralkali metal soap greases.

Applicant has found that a grease havin exceptional water resistance andhaving other properties making it a desirable grease for manyapplications can be prepared by first preparing a magnesium stearategrease, or a concentrate of magnesium stearate in oil, either bydissolving magnesium stearate in lubricating oil or by preparing themagnesium stearate in oil, and adding to this grease, at a temperatureof approximately 210 F. to 250 F., a concentrated aqueous solution ofsodium hydroxide and/ or sodium carbonate. Apparently metathesis occursforming the sodium stearate and releasing magnesium in the form of thehydroxide and/or carbonate which remains dispersed or complexed in, andbecomes a part of the final grease composition.

Thus, it is an object of this invention to provide a water-resistantmodified alkali metal soap grease and particularly a modified sodiumsoap grease, which grease has in addition to exceptional waterresistance, the desirable characteristics of relatively high meltingpoint, stability at high temperature, mechanical stability andreversibility and stability to oil separation.

A further object of this invention is to provide a method for thepreparation of a modified alkali metal soap grease and particularly asodium soap grease, which method results in the production of a greasehaving exceptional water resistance in addition to the usualcharacteristics of alkali metal soap greases.

In preparing greases of this invention, an alkaline earth metal soapgrease, as for example, a magnesium stearate grease or concentrate ofmagnesium stearate in oil, such as one containing between about andabout 50% by weight of magnesium stearate in an SAE 30 solvent-treatedWestern paratfinic mineral lubricating oil, is first produced byconventional procedures, i. e. either by dissolving magnesium stearatewhich has been separately prepared in the lubricating oil or by formingthe magnesium stearate in the oil, as for example, by reacting soprepared are either costly berates atent iii 2,831,812 Patented Apr. 221958 stearic acid with magnesium hydroxide in a small amount of oil andsubsequently adding additional oil to provide the concentration desired.The grease or concentrate so prepared is heated to a temperature ofapproximately 215 F., i. e., within the range of about 210 F. to 250 F.and to the heated grease, with agitation, is added a concentratedaqueous solution of at least one equivalent of sodium carbonate and/orsodium hydroxide per equivalent of magnesium stearate present in thegrease. Preferably, the amount of alkali metal compound added will bebetween about one and about two equivalents per equivalent of magnesiumstearate or other alkaline earth metal soap. Following the addition ofthe aqueous hydroxide and/or carbonate, additional oil may be added toproduce a finished grease of the desired soap content at a temperatureof approximately 265 F. while the mix ture is being agitated and theresulting product then heated to a maximum of 325 F. Following this heating the mixture is cooled with agitation to room temperature. As is wellknown in the art, antioxidants and/or dispersing agents may be employed.Thus, oil-soluble organic amines, such as phenyl alpha-naphthylamine,phenyl betanaphthylamine and diphenylamine may be added as oxidationinhibitors. Compounds, such as fatty acid and related esters ofpolyethylene glycols, N-substituted fatty acid amides, the substituentsbeing polyethylene glycol groups, glycerine and similar materials may beused as dispersing agents.

The properties and characteristics of greases prepared according to theprocedure described hereinabove have been determined using usual testmethods applicable to greases and the water resistance has beendetermined using various test methods. One method is to place a smalllump of the grease, approximately 3 grams, in boiling water anddetermine the time required to break down or dissolve the grease.Another method of testing consists in placing the grease in aballbearing assembly and operating the hearing at 600 R. P. M. whiledirecting a stream of water maintained at F. and/or 180 F. against thebearing for a period of 1 hour. In the first test, which will bereferred to as the boiling water test, an ordinary sodium base greasecontaining 20% by weight of sodium stearate completely disintegrated in2 minutes. In the second test, which will be referred to as the bearingtest, the same soda base grease was completely washed from the bearingat 140 F. A commercial sodium base grease prepared from a mixture oftallow and tallow fatty acids was completely washed out of the bearingeven at room temperature. On the other hand, greases prepared followingthe teachings of this invention have been found to be capable ofwithstanding 1015 minutes or more without appreciable solution ordecomposition in the boiling water test and show losses of as low asonly a few percent in the bearing test run at 180 F.

Although the greatest advantages are gained by the use of sodiumhydroxide and/or carbonate and reacting these compounds with magnesiumbase greases to produce sodium base greases containing magnesiumhydroxide and/ or carbonate in that the greases produced in this mannerare relatively cheap and have all of the characteristics desired,including exceptional water resistance, other alkaline earth metalsoaps, as for vexample, calcium, strontium and barium soaps, may besubstituted for the magnesium soaps. Moreover, potassium hydroxideand/or carbonate may be substituted for the corresponding sodiumcompounds and the resulting modified potassium greases show improvedwater resistance over typical potassium base greases and have physicalcharacteristics similar to those obtained with sodium.

3 Lithium hydroxide and/ or carbonate may, of course, be substituted forthe corresponding sodium compounds and the resulting modified lithiumbase greases have all of the desirable characteristics of the sodiumgreases of this invention. v

It is to be noted that some variation occurs in the resulting greaseswhere the various alkaline earth metal soaps are employed. Thus, it isto be noted'that the greases prepared by reacting sodium or other alkalimetal carbonate and/or hydroxide with calcium, barium or strontium soapgreases, are in some instances not as water resistant as those preparedusing magnesium soap greases although the water resistance of thesegreases is far superior to the water resistance of the correspondingalkali metal grease and thus such compositions form a part of thisinvention.

The preferred composition is a grease prepared by reacting a magnesiumbase grease with sodium hydroxide and/or carbonate. Moreover, greaseswhich are substantially equivalent to grease prepared in this manner areprepared by reacting alkali metal hydroxide and/or carbonates with amixed grease in which the soap constituent contains at least about 20%by weight of magnesium soap in combination with calcium, tium soap,preferably at least about 50% by weight of the magnesium soap should beemployed. Furthermore, where calcium, barium and strontium base greasesare employed alone or in combination with magnesium, it is preferable toemploy the alkali metal carbonate rather than the hydroxide sinceusually greater water resistance is obtained in the resulting grease.

Although stearic acid is shown as the saponifiable material to beemployed, other fatty acid materials may be substituted for stearicacid, provided the fatty acid materials contain at least about 90 to 95%by weight of saturated high molecular weight fatty acids. Other acidsand acid mixtures which may be employed, therefore, include hydrogenatedfatty acid mixtures, such as hydrogenated tallow fatty acids,hydrogenated fish oil acids and the like. It is to be noted that greasesprepared using oleic acid, which is an unsaturated acid, do not possessthe water resistance desired. However, a grease prepared using 90%stearic acid and oleic acid does have a water resistance substantiallyequal to that obtained using stearic acid alone. Where the percentage ofoleic acid is permitted to rise above about 10% the resulting greasesshow inferior water resistance.

barium or stron- Fatty acids having hydroxyl substituents may also beemployed. Thus, 12-hydroxy stearic acid is a satisfac tory soap stockalthough there does not appear to be any appreciable advantage inemploying such hydroxy fatty acid materials over the correspondingnon-hydroxy fatty acid.

The following examples illustrate various aspects of the invention butit is to be understood that the invention is not to be limited to theparticular combinations of metals indicated in these examples nor to thespecific conditions set forth. In many of the compositions shown in theexamples the dispersing agents are referred to as Ethofats or Ethomids.These compounds are made by Armour Chemical Division, Armour andCompany, Chicago, Illinois. The Ethofats are mono-fatty or resinacidesters of polyethylene glycols. Ethofat 242/25 is a rosin fatty acidester of polyethylene glycol having ap proximately 15 ethylene glycolunits per molecule.

the-fat 60/ i5 is a stearic acid ester of polyethylene glycol havingapproximately 5 ethylene glycol units per molecule. .Ethomid C/25 is anN-substituted coco fatty acid amide, the substituents being polyethyleneglycol having approximately 15 ethylene glycol units per molecule.

Example I A grease was prepared using the following materials: GramsMagnesium stearate 282 Sodium hydroxide (97%) 41.5 Ethofat 242/25 1Sgrams of water was added dropwise while mixing. A

heavy dough formed as the sodium hydroxide was being added. The productwas mixed and heated while adding the remainder of the mineral oil andthen heated to a temperature of 325 F. At this point, the phenylalphanaphthylamine was added and the grease cooled to room temperaturewhile mixing. The finished grease had an A. S. T. M. worked penetrationof 335 at 77 F. and contained 18.5% by weight of soap calculated assodium stearate. A small lump of this grease broke down after 15 minutesin the boiling water test. In the bearing test the loss was 2.5% at F.and 42.1% at 180 F.

Phenyl alpha-naphthylamine 6 SAE 30 lubricating oil 1050 The magnesiumoxide was slurried with 300 grams of mineral oil, stearic acid was addedand the mixture heated to 285 F. At this point Ethcfat was addedtogether with an additional 100 grams of mineral oil and the mixturecooled to 240 F. The sodium carbonate, dissolved in grams of hot water,was then added slowly while mixing and when a heavy dough formed,heating was resumed. At 265 F. an additional 400 grams of mineral oilwas added as rapidly as the mixture would absorb it smoothly andfollowing the completion of the oil addition, the temperature was raisedto 325 F. The grease was then cooled while adding the phenylalpha-naphthylamine and the remaining oil, and mixingwas continued untilthe grease reached room temperature. The grease prepared in this mannerhad an A. S. T. M. penetration of 298 at 77 F. and contained 20.6% byweight of soap calculated as sodium stearate. A small lump of thisgrease did not entirely break down after 1 hour in the boiling watertest and in the bearing test the loss at 180 F. was 4.8%. The droppingpoint of the grease determined by the rapid dropping point method was330 F.

Example 111 A grease was prepared from the following materials using aprocedure similar to that described in Example ll.

The resulting grease had a worked A. S. T. M. penetra tion at 77 F. of292, a rapid dropping point of 360 F. and contained approximately 19.5%soap calculated as sodium stearate. The loss in the bearing test was 23%at 180 F.

Example IV Example III was repeated with the exception that Ethofat 60/and the phenyl alpha-naphthylamine were eliminated from the composition.The resulting grease was very similar to that produced in Example III.In the bearing test at 180 F. the loss amounted to 24%.

Example V A grease was prepared from the following materials using theprocedure set forth in Example II.

Grams Stearic acid 270 Magnesium oxide 40 Sodium carbonate (anhydrous)55 Sodium hydroxide (97%) 12 Ethofat 60/15 15 Phenyl alpha-naphthylamine6 SAE 30 lubricating oil 1700 The sodium hydroxide was added as anaqueous solution immediately after the addition of sodium carbonate. Theresulting grease had a worked A. S. T. M. penetration at 77 F. of 286, arapid dropping point of 380 F., and contained 14.1% by weight of soapcalculated as sodium stearate. A small lump of this grease did notcompletely dissolve in boiling water in 1 hour. The loss in the bearingtest at 180 F. was 23.8%.

Example VI For purposes of comparison with the grease made using steaiicacid, a grease similar to that prepared in Example V was made usingolcic acid in place of the stearic acid. The resulting grease wastypical of those which have been prepared with unsaturated fatty acidsas the only acids present in the composition. The grease was preparedwith the following materials following the procedure out- 1 A Westernsolvent-treated paratfinic mineral lubricating oil.

The resulting product had a worked A. S. T. M. penetration of 275 and asoap content calculated as sodium oleate of 18.5%. This grease showedlosses of 92% and 81%, respectively, in the hearing test at 180 F.

Example VII A grease was prepared from the following materials using theprocedure outlined in Example III.

Grams Stearic acid 270 Calcium hydroxide (90%) 22 Magnesium oxide 22Sodium carbonate (anhydrous) 55 Sodium hydroxide (97%) H 12 Ethofat C/15 15 Phenyl alpha-naphthylamine 6 SAE lubricating oil 1300 This greasehad an unworked A. S. 'l. M. penetration of 274, a rapid dropping pointof 330 F. and contained 17.6% by weight of soap calculated as sodiumstearate. The loss in the hearing test at 180 F. was 0.74%.

Example VIII A grease was prepared using the following materials GramsStearic acid 270 Calcium hydroxide 42 Sodium carbonate (anhydrous) 55Ethofat 60/15 l5 Phenyl alpha-naphthylamine 6 SAE 30 lubricating oil1400 This grease had a worked A. S. T..M. penetration of 290 andcontained 16.7% by weight of soap calculated as sodium stearate. Theloss in the bearing test at F. was 2%. This grease sample showed someoil separation on standing.

Example IX A grease was prepared from the following ingredients:

Grams Hydrogenated fish oil acids 310 Calcium hydroxide (90%) 33 Sodiumcarbonate (anhydrous) 55 Sodium hydroxide (97%) 16 Ethomid C/25 15Phenyl alpha-naphthylamine 6 SAE 30 lubricating oil 1300 Theresultinggrease had a Worked A. S. T. M. penetration at 77 F. of 290 andcontained 19.3% by weight of soap calculated as sodium soap. the lossamounted to 36% at 180 F.

Example X A grease prepared as described in Example Iii using anequivalent amount of potassium carbonate in place of the sodiumcarbonate was a water resistant grease.

Example XI A grease prepared as described in Example III substituting anequivalent amount of lithium hydroxide for the sodium carbonate showed aloss of less than 10% in the bearing test at 180 F.-

Example XII For purposes of comparison with the greases of thisinvention, a grease was prepared in which a sodium soap grease was firstformed and to the sodium grease was added approximately one equivalentper equivalent of sodium soap of magnesium hydroxide. The followingmaterials were employed:

In the hearing test Grams Stearic acid 270 Sodium hydroxide (97%) 42Magnesium hydroxide 30 Ethofat 60/ 15 15 Phenyl alpha-naphtylamine 6 SAE20 lubricating oil 900 A mixture of stearic acid, Ethofat and 400 gramsof oil was heated to 210-220 F. and to this solution was added asolution of the sodium hydroxide in approximately 55 grams of water.Heating and mixing was continued to effect saponification and then themagnesium hydroxide slurried in 38 grams of water was added slowly whileagitating the grease mixture. The heating and mixing was continued whilethe temperature was increased to 265 F. and at this time the remainderof the oil was added. The resulting product was heated to 332 F,

e phenyl alpha-napthylamine added and the batch cooled to roomtemperature while continuing the mixing.

The resulting grease contained approximately 23% by weight of soapcalculated as sodium soap, had a rapid dropping point of 365 F. and anA. S. T. M. penetration at 77 F. of 300. In the bearing test the greasewas completely washed out of the hearing at 180 F It will be seen fromthe above that a soda base grease containing magnesium hydroxideprepared by adding the magnesium compound to the sodium grease is notwater resistant and requires a higher soap content to give -a grease ofthe same physical characteristics as those prepared by metathesizingmagnesium base greases with sodium hydroxide or carbonate.

In the above description and in the above examples it is shown that theaqueous solution of alkali metal hydroxide or carbonate is added to thealkaline earth metal grease at a temperature within about 210 F. and 250F. It is to be pointed out, however, that this temperature range is notcritical and that the addition may be made at lower or highertemperatures. The indicated range, however, is the preferable range, inthat at tempera tures below about 210 F. the alkaline earth metal greaseis too stiff to work readily in a kettle and thus it is difiicult toobtain the desired dispersion of the aqueous solution in the grease.Moreover, at temperatures above about 250 F. it is sometimes moredifiicult to control foaming.

Following the addition of aqueous hydroxide or carbonate, the finalgrading with oil is shown to be accomplished at a temperature of about265 F. Again this temperature is not critical since the final quantitiesof oil may be added at temperatures higher or lower than the indicatedtemperature without alfccting the characteristics of the finishedgrease. This particular temperature is merely a convenient temperatureat which to carry out this operation. At about this temperature or athigher temperatures the grease seems to absorb oil more readily than atlower temperatures.

It is to be noted also that the maximum temperature to which any of thegreases shown were heated has been indicated to be about 325 F. Theobject of heating to about this temperature is to remove water since itis desired that the finished grease be substantially anhydrous, i. e.,that it contain less than about 1-2'% by weight of water and preferablyless than 0.5% water. Greases prepared following the principles of thisinvention, which have been heated to as high as 400 F. and then cooledwhile mixing, have been found to have the same characteristics,including high water resistance, as corresponding compositions heated toonly 325 F. Moreover, it is not necessary to heat to a temperature ashigh as 325 F. to effect dehydration, providing the heating period isextended to insure reasonably complete removal of water. Thus, entirelysatisfactory greases have been finished at temperatures as low as 300 F.

The percentage of soap, calculated as the alkali metal soap, in thefinal grease compositions of this invention will generally be betweenabout 10% and about 30 or 40% by weight of the total compositionalthough lower soap contents, such as about have been found to besatisfactory in some cases. The amount of antioxidant to be employed mayvary between 0.1% and about 1% by weight and the amount of dispersingagent may vary between about 0.1% and about 1.5% by weight, however, asindicated above-the use of these auxiliary agents is not an essentialfeature of the invention. These auxiliary agents may be added at anypoint in the procedure, however, generally the antioxidant will be addedalong with, or following, the addition of the final quantities of oil.

I claim:

1. A water-resistant grease prepared by reacting a mixture of minerallubricating oil and alkaline earth metal soap of fatty acids containingat least about 90% by weight of saturated high molecular weight fattyacids with an aqueous solution of between about 1 and about 2equivalents, per equivalent of alkaline earth metal soap, of a compoundselected from the class consisting of alkali metal hydroxides andcarbonates and heating the resulting mixture to remove water.

2. A water-resistant grease consisting of mineral lubricating oilcontaining between about 5% and about 40% by weight of soap prepared byreacting an alkaline earth metal soap grease with between about 1 andabout 2 equivalents, per equivalent of alkaline earth metal soap, of analkali metal compound selected from the class consisting of alkali metalhydroxides and carbonates in the presence of a small amount of water andheating the resultant product to eflect dehydration, said alkaline earthmeal soap being a fatty acid soap in which said fatty acid is at leastabout saturated high molecular weight fatty acid.

3. A grease according to claim 2 in which said alkaline earth meal soapgrease is a magnesium soap grease.

4. A grease according to claim 2 in which said alkali metal compound isa sodium compound.

5. A grease according to claim 4 in which said sodium compound is sodiumhydroxide.

6. A grease according to claim 2 in which said alkali metal compound isa potassium compound.

7. A grease according to claim 2 in which said alkaline earth metal soapcontains at least about 20% by weight of magnesium soap.

8. A grease according to claim 2 containing also between about 0.1% andabout 1.5% by weight of a dispersing agent of the class consisting ofesters of polyethylene glycols, polyethylene glycol-N-substituted fattyacid amides and glycerine.

9. A grease according to claim 2 containing also between about 0.1% andabout 1% by weight of an oilsoluble organic amine as an antioxidant.

10. A water-resistant, modified sodium base grease consisting of minerallubricating oil containing between about 5% and about 40% by weight of asoap prepared by reacting a mixture of oil and magnesium soap ofsubstantially saturated high molecular weight fatty acids with betweenabout 1 and about 2 equivalents of sodium hydroxide per equivalent ofmagnesium soap in the presence of a small amount of water and heatingthe resulting product to efiect dehydration.

11. A method of preparing a water-resistant grease which comprisesreacting a mixture of mineral lubricating oil and alkaline earth metalsoap of fatty acids containing at least about 90% by weight of saturatedhigh molecular weight fatty acids with an aqueous solution of betweenabout 1 and about 2 equivalents, per equivalent of alkaline earth metalsoap, of a compound selected from the class consisting of alkali metalhydroxides and carbonates and heating the resulting mixture to removewater.

12. A method of preparing a water-resistant grease which comprisesreacting an alkaline earth metal soap grease, consisting of minerallubricating oil containing between about 5% and about 40% of alkalineearth metal soap, withbetween about 1 and about 2 equivalents, perequivalent of alkaline earth metal soap, of an alkali metal compoundselected from the class consisting of alkali metal hydroxides andcarbonates in the presence of a small amount of water and heating theresultant product to effect dehydration, said alkaline earth metal soapbeing a fatty acid soap in which said fatty acid is at least about 90%saturated high molecular weight fatty acid.

13. A method according to claim 12 in which said alkaline earth metalsoap grease is a magnesium soap grease.

14. A method according to claim 12 in which said alkali metal compoundis a sodium compound.

15. A method according to claim 14 in which said sodium compound issodium hydroxide.

16. A method according to claim 14 in which said sodium compound issodium carbonate.

17. A method according to claim 12 in which said alkali metal compoundis a lithium compound.

18. A method according to claim 12 in which said fatty acid compriseshydroxy stearic acid.

19. A method according to claim 12 in which about 0.1% to about 1.5% byweight of a dispersing agent of 9 the class consisting of esters ofpolyethylene glycols, polyethylene glycol-N-substituted fatty acidamides and glycerine is added at some point in the preparation.

20. A method according to claim 12 in which about 0.1% to about 1% byweight of an oil-soluble organic amine is added at some point in thepreparation.

10 References Cited in the file of this patent UNITED STATES PATENTSClarke Nov. 26, 1940 Morway et a1. July 4, 1950 Peterson May 5, 1953OHalloran June 9, 1953 OHalloran July 21, 1953

1. A WATER-RESISTANT GREASE PREPARED BY REACTING A MIXTURE OF MINERALLUBRICATING OIL AND ALKALINE EARTH METAL SOAP OF FATTY ACIDS CONTAININGAT LEAST ABOUT 90% BY WEIGHT OF SATURAATED HIGH MOLECULAR WEIGHT FATTYACID WITH AN AQUEOUS SOLUTION OF BETWEEN ABOUT 1 AND ABOUT 2EQUIVALENTS, PER EQUIVALENT OF ALKALINE EARTH METAL SOAP, OF A COMPOUNDSELECTED FROM THE CLASS CONSISTING OF ALKALI METAL HYDROXIDES ANDCARBONATES AND HEATING THE RESULTING MIXTURE TO REMOVE WATER.